1. Field of the Invention
A common problem in areas where freezing temperatures occur is a tendency for bridges to freeze over while the roads on either side of the bridge remain unfrozen. This is because the bridge deck cools very quickly while the roadbed is both insulated and warmed by the earth upon which it rests. Since bridge decks freeze over sooner than the rest of the highway, the unwary motorist is faced with a very real hazard.
To combat the hazard presented by frozen bridge decks, highway maintenance crews often spread a salt such as sodium chloride or calcium chloride on the surface of the bridge. While salting reduces this hazard, it creates the problem of salt water. Bridge decks, normally constructed with Portland cement concrete, are somewhat porous. The salt water diffuses into this porous material. When it reaches the metal reinforcing bars within the concrete, corrosion occurs. Corrosion causes an increase in volume of the reinforcing metal. The resulting pressure on the concrete results in popouts and delaminations, sometimes over very large areas. The salt water also causes scaling which is a form of surface erosion. When the damage is severe enough, complete reconstruction of the bridge deck is required. This can involve removal of the old bridge deck and replacement with an entirely new deck. Where concrete supporting pillars are used, complete demolition and reconstruction of the bridge may be necessary.
Similar problems occur wherever decks and the like are supported above ground and are exposed to freezing temperatures such as in multilevel car parking facilities.
Since the major problem is salt water seeping into the porous structure, sealing coats have been applied to bridge decks and the like to "seal out" the salt water. A problem experienced in applying these seal coats is bubble formation in the coating. This problem is particularly severe with concrete containing high percentages of entrained air. Before the mid-1960's concrete bridge decks contained very little air, usually less than 4%. Since then, concrete, particularly that used to form bridge decks, was required to have about 6 to about 6.5% entrained air to provide resistance to scaling. Seal coats applied over concrete containing these high percentages of air suffer severe air bubble formation problems. The bubbles are very difficult to remove and in most cases their removal destroys the integrity of the seal coat. On the other hand, if the bubbles are not removed the seal coat is considerably weakened at these points.
Bubble formation is not such a severe problem with preformed membranes which are "glued" into place. However, these require considerable labor, are subject to wrinkling problems during application and in some cases are subject to adhesion problems with asphalt concrete overlays.
What is needed is a low cost sealing composition which is inexpensive to install, tough, impermeable to salt water and not subject to bubble formation.
This invention is directed toward such a surfacing composition for bridge decks and the like. It is competitive in cost with other seal coat systems, tough, durable, impermeable to salt water and subject only to very minimal bubble formation. In addition when applied to surfaces, whether or not porous, it provides an excellent sound deadening effect.